Insufficient neovascularization, characterized by poor vessel growth, is a major contributor to the pathogenesis of ischemic heart disease and limits the capacity of cardiac tissue preservation and regeneration. The E2F transcription factors are key regulators of cell growth and survival. Specifically, E2F1 is a transcriptional activator that, when overexpressed, induces quiescent cells to proliferate. However, accumulating evidence also indicates that, beyond cell cycle regulation, E2F1 has diverse physiological functions that are specific to tissue type and biological context. We have recently reported the following: A) Loss of E2F1 enhances angiogenesis in surgically induced hindlimb ischemia and accelerates the recovery of blood flow, indicating that E2F1 is an angiogenic inhibitor; B) The primary cause of the enhanced angiogenesis observed in E2F1-deficient mice appears to be the overproduction of vascular endothelial growth factor (VEGF), and E2F1 suppresses the transcription of VEGF; C) Oncogene p53 may also play a role in this E2F1- mediated hypoxic regulation of VEGF expression and resulting modulation of angiogenesis. However, neither the molecular mechanisms governing E2F1-mediated VEGF suppression nor the contributions of the intracellular association and crosstalk between E2F1 and p53 in VEGF-induced angiogenesis have been elucidated. In addition, our follow-up preliminary studies indicate that loss of E2F1 not only leads to an increase in VEGF expression but also significantly enhances the migratory capacity of bone marrow-derived endothelial progenitor cells (BM EPCs) under hypoxic conditions. It is our central hypothesis that E2F1 regulates neovascularization by modulating both p53-dependent VEGF gene expression and EPC activity, and thereby impacts the functional outcome of myocardial infarction. This hypothesis will be tested by the following specific aims: 1) to investigate molecular mechanisms of E2F1-mediated p53-dependent regulation of VEGF transcription; 2) to elucidate the role of E2F1-regulated neovascularization in the recovery of heart function after myocardial infarction; 3) to define the role of E2F1 in BM EPC-mediated vasculogenesis in the ischemic myocardium. We anticipate that the experiments proposed in this project will provide a critical framework for understanding the mechanisms that underlie E2F1-mediated regulation of neovascularization and the functional significance of E2F1 in ischemic heart disease, which could potentially aid the development of novel therapies for ischemic diseases.